Design of a new high repetition rate Nd:YAG Thomson scattering system for Heliotron J

A new high repetition rate Nd:YAG Thomson scattering system has been designed for the Heliotron J helical device. The main purpose of installing the new Thomson scattering system is an investigation of an improved confinement physics such as the edge transport barrier (H-mode) or the internal transport barrier of the helical plasma. The system has 25 spatial points with ∼ 10 mm resolution. Two high repetition Nd:YAG lasers ( > 550 mJ at 50 Hz ) realize the measurement of the time evolution of the plasma profile with 10 ms time interval. Scattered light is collected with a large concave mirror ( D = 800 mm , f / 2.25 ) with a solid angle of ∼ 100 msr . The laser beam is injected from obliquely downward to upward, and obliquely backscattered light is detected (scattering angle is 20°). Model simulation of the polychromator shows the measurable electron temperature and density range are from10 eV to 10 keV, > 5 × 10 18 m − 3 within 3% error for the temperature measurement, respectively.